In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Currently available cutting elements utilized in shear cutter bits use superabrasive materials having Knoop hardness greater than 2000 such as, but not limited to, single crystal diamond, polycrystalline diamond (PCD), thermally stable polycrystalline diamond, CVD diamond, metal matrix diamond composites, ceramic matrix diamond composites, nanodiamond, cubic boron nitride, and combinations of superabrasive materials. The superabrasive layer or table is supported by or joined coherently to a substrate, post or stud that is generally made of cobalt tungsten carbide (Co—WC). The overall shape is generally cylindrical. The relative position of the diamond table to the Co—WC stud is directly on the top. From the side view of the overall structure is a layered structure with the diamond table forming the top portion and the Co—WC stud forming the bottom portion.
FIG. 13A is an example of a traditional shear cutter bit 100 including at least one traditional cutting element 102 that includes a superabrasive material 104 and a substrate 106. The cutting element 102 is brazed or pressed into the shear cutter bit 100 for subterranean formation drilling. The cutting element 102 is mounted into the shear cutter bit 100 at a certain angle which is called the back-rake angle β. The back-rake angle β is the angle between the shear cutter bit axis 110 and the front surface 112 of the superabrasive material. The back-rake angle in many shear cutter bits is between about 15° and about 25°, but can be as high as 30° or even 45°.
As illustrated in FIG. 13A, the cutting element will plow and shear the bottom of the hole in the subterranean formation 108 during the cutting operation. As illustrated in FIG. 13B, after a certain period of drilling, the cutting element will generally have a wear pattern or wear surface 114 with a wear angle γ that is approximately equal to the back-rake angle β. The wear angle γ is the angle between the cutting element longitudinal axis 116 and the wear surface 114.
FIG. 14 illustrates a top perspective view of the cutting element 102 after it has been removed from the shear cutter bit 100, because of wear. The wear surface 114 extends into the substrate 106 at the wear surface bottom 118.
Cutting element abrasion resistance performance can be measured by Vertical Turret Lathe with Coolant (VTL-c) testing in which a granite log is machined by a cutting element The abrasion resistance performance is graphically presented with the cutting element wear volume plotted on the vertical axis and the linear distance the cutting element has traveled through the granite log along the horizontal axis. Plots of VTL-c testing results for traditional cutting elements have an inflection when the cutter element wear volume begins to accelerate quickly in relation to the linear distance. Further, it has been determined that the inflection generally correlates to the event when the wear surface (114) extends beyond the superabrasive table and beyond the interface between the superabrasive material and substrate. It appears the inflection develops because the heat generated by the friction of the substrate, especially Co—WC, against the rock in the subterranean hole degrades or damages the superabrasive material and makes the cutting element more vulnerable to abrasion failure.
It has further been determined that the inflection and accelerated cutter insert wear can be delayed by increasing the thickness of the superabrasive material. However, simply increasing the thickness of the superabrasive table leads to increased stress in the superabrasive material from the thermal expansion coefficient mismatch with the Co—WC substrate during and after the high pressure high temperature (HPHT) sintering process. The thermal expansion coefficient mismatch can lead to failure of the superabrasive material from horizontal cracks or delamination. In particular, commercial cutting elements have a superabrasive material limited to no more than 3 millimeters thick to avoid the delamination and failure concerns.